In such tool assemblies the tool holder is installed on a power driven machine, and the tool is a cutting tool, an adaptor for holding tools or any other means required for performing a metal working operation. The clamping mechanism provides a means for quickly changing tools during the metal working operations.
The coupling mechanism has the main objectives of transferring torque by, inter alia, frictional force from a spindle via the tool holder to the tool while maintaining alignment between the rotational axes of the tool and spindle. In order to achieve these objectives, the shank of the tool and the socket of the tool holder are typically formed with compatible conical geometries, while a collet and coupling member ensure “full coupling” between these geometries. “Full coupling” is defined as contact of about 70% of the length between the shank and socket faces and is achieved by the following two conditions. First, the diameters of the shank and socket, at their widest ends and narrowest ends, must not exceed their required dimensions by more than several microns. Second, a significant drawing force has to be applied via the collet onto the coupling member. Typically, the shank is hollow and the periphery walls of the socket are designed to be resilient in order to enable the required elastic deformation for “full coupling”.
U.S. Pat. No. 6,079,919 describes a clamping mechanism wherein the shank has a cone shape which corresponds to the internal cone shape of the socket. A high tensile force ensures “full coupling” between the shank and socket. In order to ensure alignment of rotational axes between the spindle and tool, tight tolerances must be maintained during manufacturing of the shank and socket. In this type of clamping mechanism, any error occurring during manufacturing or any obstruction such as dirt or a metal chip caught between the shank and socket will cause miss alignment.
Another example of a clamping mechanism is described in U.S. Pat. No. 5,407,308. The coupling between the shank and socket occurs in two regions: in a region of a tapered portion adjacent a wider end of the shank and in a region of a cylindrical portion adjacent a narrower end thereof The short tapered portion of the shaft extends over approximately a ⅓ of the axial length of the socket. As a result, a relatively smaller force is required in order to ensure “full coupling”. However, in order to ensure alignment of rotational axes between the spindle and tool, tight manufacturing tolerances are still required during manufacturing of the tapered and cylindrical portions of the shaft and socket.
It is an object of the present invention to provide a clamping mechanism that significantly reduces or overcomes the aforementioned disadvantages.